| TLC | Total lung capacity: the volume in the lungs at maximal inflation |
|---|---|
| RV | Residual volume: the volume of air remaining in the lungs after a maximal exhalation |
| ERV | Expiratory reserve volume: the maximal volume of air that can be exhaled from the end-expiratory position |
| IRV | Inspiratory reserve volume: the maximal volume that can be inhaled from the end-inspiratory level |
| IC | Inspiratory capacity: the sum of IRV and TV |
| IVC | Inspiratory vital capacity: the maximum volume of air inhaled from the point of maximum expiration |
| VC | Vital capacity: the volume equal to TLC − RV |
| VT | Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol VT or VT is used.) |
| FRC | Functional residual capacity: the volume in the lungs at the end-expiratory position |
| RV/TLC% | Residual volume expressed as percent of TLC |
| VA | Alveolar gas volume |
| VL | Actual volume of the lung including the volume of the conducting airway. |
| FVC | Forced vital capacity: the determination of the vital capacity from a maximally forced expiratory effort |
| FEV1 | Volume that has been exhaled at the end of the first second of forced expiration |
| FEFx | Forced expiratory flow related to some portion of the FVC curve; modifiers refer to amount of FVC already exhaled |
| FEFmax | The maximum instantaneous flow achieved during a FVC maneuver |
| FIF | Forced inspiratory flow: (Specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. For example, maximum inspiratory flow is denoted FIFmax. Unless otherwise specified, volume qualifiers indicate the volume inspired from RV at the point of measurement.) |
| PEF | The highest forced expiratory flow measured with a peak flow meter |
| MVV | Maximal voluntary ventilation: volume of air expired in a specified period during repetitive maximal effort |
| Pulmonary Function Testing | |
|---|---|
| Diagnostics | |
| MeSH | D012129 |
| OPS-301 code | 1-71 |
Pulmonary Function Testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment.[1] Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFT's are performed by a Pulmonary scientist who typically hold credentialing as a Registered Pulmonary Function Technician, a Certified Pulmonary Function Technician or a Registered Respiratory Therapist.
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Pulmonary function testing is a diagnostic and management tool used for a variety of reasons.
Neuromuscular disorders such as Duchenne muscular dystrophy are associated with gradual loss of muscle function over time. Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to atelectasis (the ability of the lungs to gain oxygen) and an overall insufficency in lung strength.[2] A combination of reduced lung compliance caused by generalized and widespread microatelectasis and chest wall deformity caused by increased chest wall compliance4 results in increased work of breathing and chronic respiratory insufficiency.[3] Musculoskeletal deformities such as kyphoscoliosis contribute to restrictive lung disease.
Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.[4]
Spirometry includes the tests of pulmonary mechanics, the measurements of FVC, FEV1, FEF values, forced inspiratory flow rates (FIFs), and the MVV. Measuring pulmonary mechanics is assessing the ability of the lungs to move large volumes of air quickly through the airways to identify airway obstruction.
Spirometry is a safe procedure however there is cause for concern regarding untoward reactions. The value of the test data should be weighed against potential hazards. Some complications have been reported such as; pneumothorax, increased intracranial pressure, syncope, chest pain, paroxysmal coughing, nosocomial infections, oxygen desaturation, and bronchospasm.
There are four lung volumes and four lung capacities. A lung capacity consists of two or more lung volumes. The lung volumes are tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). The four lung capacities are total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity (FRC) and the vital capacity (VC).
Measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically. Maximal inspiratory pressure (MIP) is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece. Maximal expiratory pressure (MEP) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation. Repeated measurements of MIP and MEP are useful in following the course of patients with neuromuscular disorders.
Measurement of the single-breath diffusing capacity for carbon monoxide (DLCO) is a fast and safe tool in the evaluation of both restrictive and obstructive lung disease.
The six-minute walk test is a good index of physical function and therapeutic response in patients with chronic lung disease, such as COPD or idiopathic pulmonary fibrosis[5][6][7]
Arterial blood gases (ABGs) are a helpful measurement in pulmonary function testing in selected patients. The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced COPD.
An elevated serum bicarbonate level, or chronic hypoxemia. ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.
The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit.[8] This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed spirometer, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.
The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.[9]
The plethysmography technique applies Boyle's law and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.[10]
Changes in lung volumes and capacities are generally consistent with the pattern of impairment. TLC, FRC and RV increase with obstructive lung diseases and decrease with restrictive impairment.
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